1. Field of the Invention
The present invention relates to an apparatus for evaluating the characteristics of a photosensitive drum for electrophotography, and, more particularly, to an apparatus, a structure and a method capable of improving the accuracy in evaluating the characteristics of the same.
2. Related Art Statement
When a photosensitive drum for use in electrophotography is delivered, a variety of characteristics such as the charge, the dark damping, the optical damping and the fatigue of the manufactured photosensitive drum must be measured to evaluate whether or not the characteristics of the manufactured photosensitive drum meet predetermined standard ranges. Accordingly, a characteristics evaluating apparatus has been used to evaluate the above-described characteristics in a sampling inspection manner.
A characteristics evaluating apparatus of the type described above has been composed of a process drive portion A, an exposure light source portion B, a control portion C, and an independent computer system portion D and the like. Furthermore, the above-described elements A, B, C and D respectively comprise:
The process drive portion A comprises a drive portion such as a motor for rotating a photosensitive member such as a photosensitive drum, a charging/discharging portion disposed to confront the surface of the photosensitive drum, and a charged potential measuring probe. The exposure light source B comprises an exposure light source, a light control diaphragm portion, a mirror and an exposure control portion. The control portion C comprises a control portion for controlling the rotation of the motor of the process drive portion A, a main power source portion, a high voltage power source portion for the charging operation, a measurement control portion and a lamp power source portion.
Furthermore, the computer system portion D has a function of transmitting, to the units, automatically setting outputs for setting exposure energy, the quantity of charge, the rotational and movement speed of the photosensitive member and the measurement position for measuring the surface potential. In addition, the computer system portion D has a function of subjecting the various characteristics obtained by the measurements and corresponding reference values to comparisons and transmitting and display, for example, the deviations of the measured values.
However, the above-described conventional characteristics evaluating apparatus suffers from a problem of an erroneous result in the potential measurement or another problem of scatter in measured values if, for example, the same measuring point is not measured even if the same photosensitive drum is measured.
The above-described characteristics evaluating apparatus according to the conventional technology is arranged in such a manner that the process drive portion A, the exposure light source portion B and the control portion C are accommodated in the same space in a case formed into a dark box. Therefore, although an adverse influence of external light upon the exposure of the photosensitive drum can be eliminated, another adverse influence of light leaked from the exposure light source portion upon the photosensitive drum cannot be eliminated. What is even worse, the measured values of the surface potential will easily scatter because the quantity of leaked light can be changed depending upon the set condition of the exposure light quantity. Furthermore, the measured values scatter because the quantity of leaked light is changed depending upon the employed characteristics evaluating apparatus. In addition, the temperature in the case rises with time due to heat generated in the exposure light source portion B and that generated in the light source portion of the control portion C. Therefore, the characteristics cannot easily be evaluated under a constant temperature condition and the scatter in the measured values cannot be prevented.
Then, the process drive portion A and the exposure light source portion B of the conventional characteristics evaluating apparatus will now be described with reference to FIG. 1.
The process drive portion A comprises a supporting frame a1 to which the photosensitive drum 1, the characteristics of which must be measured, is fastened, a rotation drive source a2 for rotating the photosensitive drum 1, a charging portion a3 for charging the entire surface of the photosensitive drum 1 by a corona discharging wire disposed to confront the overall length of the surface of the fastened photosensitive drum, a discharging portion a4 for discharging it after the measurement has been completed, a potential measuring probe a5, a screw shaft a5' for moving the potential measuring probe a5 in the lengthwise direction of the photosensitive drum 1 for the overall length of the same, a supporting member a5" screwed to it, a drive source a6 for rotating the screw shaft a5' and an illuminance measuring probe a7 secured adjacent to the portion of the surface of the photosensitive drum 1 to which light is applied in such a manner that the illuminance measuring probe a7 confronts the photosensitive drum 1.
The exposure light source portion B, for example, comprises a light source b1, a monochrometer (spectrometer) b3, a light control diaphragm b4 and a reflecting mirror b5.
The above-described characteristics evaluating apparatus according to the conventional technology evaluates the electrostatic characteristics in the lengthwise direction of the photosensitive drum 1 in such a manner that the photosensitive drum 1 is rotated and the charging portion a: and the exposure light source portion B secured adjacent to the photosensitive drum 1 charge and expose the entire surface of the photosensitive drum 1. Then, the potential measuring probe a5 is moved in the lengthwise direction of the photosensitive drum 1 at proper speed to measure the surface potential so that the measured value is subjected to a comparison with a reference value stored in the computer system portion and thus the evaluation is made.
However, since the light incidental position from the exposure light source portion B upon the photosensitive drum 1 is fixed, the exposure light quantity applied to the photosensitive drum 1 cannot easily be equalled on the entire surface in the lengthwise direction of the photosensitive drum 1. For example, in a case where light is made incident upon the central portion of the photosensitive drum, the surface of the central portion of the photosensitive drum 1 positioned at the shortest distance from the exposure light source portion B as designated by an alternate long and short dash line of FIG. 2 displays the largest exposure light quantity. The same becomes smaller and uneven in inverse proportion to the sideward distances.
Therefore, the surface potential of the exposed photosensitive drum becomes uneven in such a manner that the same is the lowest in the central portion and is enlarged in proportion to the sideward distance from the central portion as designated by a dashed line of FIG. 2. Therefore, the detection output of the potential obtained by the potential measuring probe a5 arranged to be movable in the overall length of the photosensitive drum 1 is evaluation data including the potential change due to the above-described reasons, causing an error to take place in the evaluation.
In order to make an accurate evaluation by using the characteristics evaluating apparatus, charging of the photosensitive drum must be always performed at a longitudinally even and predetermined value. Furthermore, a predetermined quantity of light must always be applied from the exposure light source portion B to surface of the photosensitive drum 1 during the measurement operation.
Accordingly, in order to maintain a predetermined light quantity, the conventional technology has employed a method, as schematically shown in FIG. 3, arranged in such a manner that light emitted from the exposure light source portion B is applied to the surface of the photosensitive drum 1 via a shutter 5 and the degree of opening of the shutter 5 is controlled by, for example, a set output supplied from the computer system D.
However, the above-described method encounters a problem in that the quantity of light applied to the photosensitive drum cannot be made uniform because the degree of opening of the shutter 5 is made to be a constant degree regardless of the change in the light quantity due to deterioration in, for example, the exposure light source portion B. What is even worse, another problem takes place in that the undesirable change in the light quantity cannot immediately be modified if the same is changed during the exposure operation due to the change in the voltage to be supplied to the exposure light source portion B and thereby generation of an error in the evaluation result cannot be prevented.